#!/usr/bin/env python
'''
parse a MAVLink protocol XML file and generate a Node.js javascript module implementation

Based on original work Copyright Andrew Tridgell 2011
Released under GNU GPL version 3 or later
'''
from __future__ import print_function

from builtins import range

import os
import textwrap
from . import mavtemplate
import sys

t = mavtemplate.MAVTemplate()


def get_mavhead(xml):
    return ("mavlink20" if xml.protocol_marker == 253 else "mavlink10")

def get_mavprocessor(xml):
    return ("MAVLink20Processor" if xml.protocol_marker == 253 else "MAVLink10Processor")

def generate_preamble(outf, msgs, args, xml):
    print("Generating preamble")
    t.write(outf, """
/*
MAVLink protocol implementation for node.js (auto-generated by mavgen_javascript.py)

Generated from: ${FILELIST}

Note: this file has been auto-generated. DO NOT EDIT
*/

jspack = require("jspack").jspack,
    _ = require("underscore"),
    events = require("events"), // for .emit(..), MAVLink20Processor inherits from events.EventEmitter
    util = require("util");

var Buffer = require('buffer').Buffer; // required in react - no impact in node
var Long = require('long');

// Add a convenience method to Buffer
Buffer.prototype.toByteArray = function () {
  return Array.prototype.slice.call(this, 0)
}

${MAVHEAD} = function(){};

// Implement the CRC-16/MCRF4XX function (present in the Python version through the mavutil.py package)
${MAVHEAD}.x25Crc = function(buffer, crcIN) {

    var bytes = buffer;
    var crcOUT = crcIN || 0xffff;
    _.each(bytes, function(e) {
        var tmp = e ^ (crcOUT & 0xff);
        tmp = (tmp ^ (tmp << 4)) & 0xff;
        crcOUT = (crcOUT >> 8) ^ (tmp << 8) ^ (tmp << 3) ^ (tmp >> 4);
        crcOUT = crcOUT & 0xffff;
    });
    return crcOUT;

}

${MAVHEAD}.WIRE_PROTOCOL_VERSION = "${WIRE_PROTOCOL_VERSION}";
${MAVHEAD}.PROTOCOL_MARKER_V1 = 0xFE 
${MAVHEAD}.PROTOCOL_MARKER_V2 = 0xFD 
${MAVHEAD}.HEADER_LEN_V1 = 6 
${MAVHEAD}.HEADER_LEN_V2 = 10 
${MAVHEAD}.HEADER_LEN = ${HEADERLEN};

${MAVHEAD}.MAVLINK_TYPE_CHAR     = 0
${MAVHEAD}.MAVLINK_TYPE_UINT8_T  = 1
${MAVHEAD}.MAVLINK_TYPE_INT8_T   = 2
${MAVHEAD}.MAVLINK_TYPE_UINT16_T = 3
${MAVHEAD}.MAVLINK_TYPE_INT16_T  = 4
${MAVHEAD}.MAVLINK_TYPE_UINT32_T = 5
${MAVHEAD}.MAVLINK_TYPE_INT32_T  = 6
${MAVHEAD}.MAVLINK_TYPE_UINT64_T = 7
${MAVHEAD}.MAVLINK_TYPE_INT64_T  = 8
${MAVHEAD}.MAVLINK_TYPE_FLOAT    = 9
${MAVHEAD}.MAVLINK_TYPE_DOUBLE   = 10

${MAVHEAD}.MAVLINK_IFLAG_SIGNED = 0x01
${MAVHEAD}.MAVLINK_SIGNATURE_BLOCK_LEN = 13

// Mavlink headers incorporate sequence, source system (platform) and source component. 
${MAVHEAD}.header = function(msgId, mlen, seq, srcSystem, srcComponent, incompat_flags=0, compat_flags=0,) {

    this.mlen = ( typeof mlen === 'undefined' ) ? 0 : mlen;
    this.seq = ( typeof seq === 'undefined' ) ? 0 : seq;
    this.srcSystem = ( typeof srcSystem === 'undefined' ) ? 0 : srcSystem;
    this.srcComponent = ( typeof srcComponent === 'undefined' ) ? 0 : srcComponent;
    this.msgId = msgId
    this.incompat_flags = incompat_flags
    this.compat_flags = compat_flags

}
""", {'FILELIST' : ",".join(args),
      'PROTOCOL_MARKER' : xml.protocol_marker,
      'crc_extra' : xml.crc_extra,
      'WIRE_PROTOCOL_VERSION' : ("2.0" if xml.protocol_marker == 253 else "1.0"),
      'MAVHEAD': get_mavhead(xml),
      'HEADERLEN': ("10" if xml.protocol_marker == 253 else "6")})

    # Mavlink2
    if (xml.protocol_marker == 253):
        t.write(outf, """
${MAVHEAD}.header.prototype.pack = function() {
    return jspack.Pack('BBBBBBBHB', [${PROTOCOL_MARKER}, this.mlen, this.incompat_flags, this.compat_flags, this.seq, this.srcSystem, this.srcComponent, ((this.msgId & 0xFF) << 8) | ((this.msgId >> 8) & 0xFF), this.msgId>>16]);
}
        """, {'PROTOCOL_MARKER' : xml.protocol_marker,
              'MAVHEAD': get_mavhead(xml)})
    # Mavlink1
    else:
        t.write(outf, """

${MAVHEAD}.header.prototype.pack = function() {
    return jspack.Pack('BBBBBB', [${PROTOCOL_MARKER}, this.mlen, this.seq, this.srcSystem, this.srcComponent, this.msgId]);
}
        """, {'PROTOCOL_MARKER' : xml.protocol_marker,
              'MAVHEAD': get_mavhead(xml)})

    t.write(outf, """

// Base class declaration: mavlink.message will be the parent class for each
// concrete implementation in mavlink.messages.
${MAVHEAD}.message = function() {};

// Convenience setter to facilitate turning the unpacked array of data into member properties
${MAVHEAD}.message.prototype.set = function(args,verbose) {
// inspect
    _.each(this.fieldnames, function(e, i) {
        var num = parseInt(i,10);
        if (this.hasOwnProperty(e) && isNaN(num)  ){ // asking for an attribute that's non-numeric is ok unless its already an attribute we have
            if ( verbose >= 1) { console.log("WARNING, overwriting an existing property is DANGEROUS:"+e+" ==>"+i+"==>"+args[i]+" -> "+JSON.stringify(this)); }
        }
    }, this);
                    //console.log(this.fieldnames);
// then modify
    _.each(this.fieldnames, function(e, i) {
        this[e] = args[i];
    }, this);
};

// trying to be the same-ish as the python function of the same name
${MAVHEAD}.message.prototype.sign_packet = function( mav) {
    var crypto= require('crypto');
    var h =  crypto.createHash('sha256');

    //mav.signing.timestamp is a 48bit number, or 6 bytes.

        // due to js not being able to shift numbers  more than 32, we'll use this instead.. 
        // js stores all its numbers as a 64bit float with 53 bits of mantissa, so have room for 48 ok. 
        // positive shifts left, negative shifts right
        function shift(number, shift) { 
            return number * Math.pow(2, shift); 
        } 

    var thigh = shift(mav.signing.timestamp,-32) // 2 bytes from the top, shifted right by 32 bits
    var tlow  = (mav.signing.timestamp & 0xfffffff )  // 4 bytes from the bottom

    // I means unsigned 4bytes, H means unsigned 2 bytes
    // first add the linkid(1 byte) and timestamp(6 bytes) that start the signature
    this._msgbuf = this._msgbuf.concat(jspack.Pack('<BIH', [mav.signing.link_id, tlow, thigh  ] ) );
 
    h.update(mav.signing.secret_key); // secret is already a Buffer
    h.update(new Buffer.from(this._msgbuf));
    var hashDigest = h.digest();
    sig = hashDigest.slice(0,6)
    this._msgbuf  = this._msgbuf.concat( ... sig ); 

    mav.signing.timestamp += 1
} 


// This pack function builds the header and produces a complete MAVLink message,
// including header and message CRC.
${MAVHEAD}.message.prototype.pack = function(mav, crc_extra, payload) {

    this._payload = payload;
    var plen = this._payload.length;
""", {'MAVHEAD': get_mavhead(xml)})

    # Mavlink2 only
    if (xml.protocol_marker == 253):
        t.write(outf, """
    //in MAVLink2 we can strip trailing zeros off payloads. This allows for simple
    // variable length arrays and smaller packets
    while ((plen > 1) && ( (this._payload[plen-1] == 0) || (this._payload[plen-1] == null) ) ) {
            plen = plen - 1;
    }
    this._payload = this._payload.slice(0, plen);
    """)

    t.write(outf, """
// signing is our first incompat flag. 
    var incompat_flags = 0; 
    if (mav.signing.sign_outgoing){ 
            incompat_flags |= ${MAVHEAD}.MAVLINK_IFLAG_SIGNED 
    } 
    // header 
    this._header = new ${MAVHEAD}.header(this._id, this._payload.length, mav.seq, mav.srcSystem, mav.srcComponent, incompat_flags, 0,);
    // payload     
    this._msgbuf = this._header.pack().concat(this._payload);
    // crc -  for now, assume always using crc_extra = True.  TODO: check/fix this. 
    var crc = ${MAVHEAD}.x25Crc(this._msgbuf.slice(1));
    crc = ${MAVHEAD}.x25Crc([crc_extra], crc);
    this._msgbuf = this._msgbuf.concat(jspack.Pack('<H', [crc] ) );

    // signing 
    this._signed     = false 
    this._link_id    = undefined 

    //console.log(mav.signing); 
    //optionally add signing 
    if (mav.signing.sign_outgoing){ 
                this.sign_packet(mav) 
    } 
    return this._msgbuf;

}

""", {'MAVHEAD': get_mavhead(xml)})

def generate_enums(outf, enums, xml):
    print("Generating enums")
    outf.write("\n// enums\n")
    wrapper = textwrap.TextWrapper(initial_indent="", subsequent_indent="                        // ")
    for e in enums:
        outf.write("\n// %s\n" % e.name)
        for entry in e.entry:
            t.write(outf, "${MAVHEAD}.${ENUMNAME} = ${ENUMVAL} // ${ENUMDESC}\n", {'ENUMNAME': entry.name,
                                                                                'ENUMVAL': entry.value,
                                                                                'ENUMDESC': wrapper.fill(entry.description),
                                                                                'MAVHEAD': get_mavhead(xml)})

def generate_message_ids(outf, msgs, xml):
    print("Generating message IDs")
    outf.write("\n// message IDs\n")
    t.write(outf, "${MAVHEAD}.MAVLINK_MSG_ID_BAD_DATA = -1\n", {'MAVHEAD': get_mavhead(xml)})
    for m in msgs:
        t.write(outf, "${MAVHEAD}.MAVLINK_MSG_ID_${MNAME} = ${MVAL}\n", {'MAVHEAD': get_mavhead(xml),
                                                                      'MNAME': m.name.upper(),
                                                                      'MVAL': m.id})

def generate_classes(outf, msgs, xml):
    """
    Generate the implementations of the classes representing MAVLink messages.

    """
    print("Generating class definitions")
    wrapper = textwrap.TextWrapper(initial_indent="", subsequent_indent="")
    t.write(outf, "\n${MAVHEAD}.messages = {};\n\n", {'MAVHEAD': get_mavhead(xml)})

    def field_descriptions(fields):
        ret = ""
        for f in fields:
            if not f.omit_arg:
                ret += "                %-18s        : %s (%s)\n" % (f.name, f.description.strip(), f.type)
        return ret

    # now do all the messages
    for m in msgs:

        # assemble some strings we'll use later in outputting ..
        comment = "%s\n\n%s" % (wrapper.fill(m.description.strip()), field_descriptions(m.fields))
        argfieldnames = []
        conststr = ""
        for f in m.fields:
            if not f.omit_arg:
                argfieldnames.append(f.name)
            else:
                conststr = conststr + "    this.%s = %s;\n" % (f.name, f.const_value)

        # instance field support copied from mavgen_python
        if m.instance_field is not None:
            instance_field = "'%s'" % m.instance_field
            instance_offset = m.field_offsets[m.instance_field]
        else:
            instance_field = "undefined"
            instance_offset = -1

        # start with the comment block
        outf.write("""
/* 
%s
*/
""" % (comment))

        # function signature + declaration
        outf.write("    %s.messages.%s = function(" % ( get_mavhead(xml), m.name.lower() ) )
        outf.write(" ...moreargs ) {\n")
        # passing the dynamic args into the correct attributes, we can call the constructor with or without the 'moreargs'
        outf.write("    [ this.%s ] = moreargs;\n" % " , this.".join(argfieldnames))
        outf.write(conststr)

        # body: set message type properties    
        outf.write("""
    this._format = '%s';
    this._id = %s.MAVLINK_MSG_ID_%s;
    this.order_map = %s;
    this.len_map = %s;
    this.array_len_map = %s;
    this.crc_extra = %u;
    this._name = '%s';

    this._instance_field = %s;
    this._instance_offset = %d;

"""     % (
        m.fmtstr, 
        get_mavhead(xml), 
        m.name.upper(), 
        m.order_map, 
        m.len_map,  
        m.array_len_map, 
        m.crc_extra, 
        m.name.upper(),
        instance_field,
        instance_offset
        ))
        
        # body: set own properties
        if len(m.fieldnames) != 0:
                outf.write("    this.fieldnames = ['%s'];\n" % "', '".join(m.fieldnames))

        outf.write("\n}\n")

        # inherit methods from the base message class
        outf.write("\n%s.messages.%s.prototype = new %s.message;\n" % ( get_mavhead(xml), m.name.lower() ,get_mavhead(xml) ) )

        orderedfields =    "var orderedfields = [ this." + ", this.".join(m.ordered_fieldnames) + "];";


        # Implement the pack() function for this message
        t.write(outf, """
${MAVHEAD}.messages.${MNAME}.prototype.pack = function(mav) {
    ${MORDERED}
    var j = jspack.Pack(this._format, orderedfields);
    if (j === false ) throw new Error("jspack unable to handle this packet");
    return ${MAVHEAD}.message.prototype.pack.call(this, mav, this.crc_extra, j );\n}\n\n""", {'MORDERED': orderedfields, 'MAVHEAD': get_mavhead(xml), 'MNAME': m.name.lower()})

  

def mavfmt(field):
    '''work out the struct format for a type'''
    map = {
        'float'    : 'f',
        'double'   : 'd',
        'char'     : 'c',
        'int8_t'   : 'b',
        'uint8_t'  : 'B',
        'uint8_t_mavlink_version'  : 'B',
        'int16_t'  : 'h',
        'uint16_t' : 'H',
        'int32_t'  : 'i',
        'uint32_t' : 'I',
        'int64_t'  : 'q',
        'uint64_t' : 'Q',
        }

    if field.array_length:
        if field.type in ['char', 'int8_t', 'uint8_t']:
            return str(field.array_length)+'s'
        return str(field.array_length)+map[field.type]
    return map[field.type]

def generate_mavlink_class(outf, msgs, xml):
    print("Generating MAVLink class")

    # Write mapper to enable decoding based on the integer message type
    t.write(outf, "\n\n${MAVHEAD}.map = {\n", {'MAVHEAD': get_mavhead(xml)});
    for m in msgs:
        outf.write("        %s: { format: '%s', type: %s.messages.%s, order_map: %s, crc_extra: %u },\n" % (
            m.id, m.fmtstr, get_mavhead(xml), m.name.lower(), m.order_map, m.crc_extra))
    outf.write("}\n\n")
    
    t.write(outf, """

// Special mavlink message to capture malformed data packets for debugging
${MAVHEAD}.messages.bad_data = function(data, reason) {
    this._id = ${MAVHEAD}.MAVLINK_MSG_ID_BAD_DATA;
    this._data = data;
    this._reason = reason;
    this._msgbuf = data;
}
${MAVHEAD}.messages.bad_data.prototype = new ${MAVHEAD}.message;

//  MAVLink signing state class
MAVLinkSigning = function MAVLinkSigning(object){ 
        this.secret_key = new Buffer.from([]) ; //new Buffer.from([ 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42 ]) // secret key must be a Buffer obj of 32 length 
        this.timestamp = 1 
        this.link_id = 0 
        this.sign_outgoing = false // todo false this 
        this.allow_unsigned_callback = undefined 
        this.stream_timestamps = {} 
        this.sig_count = 0 
        this.badsig_count = 0 
        this.goodsig_count = 0 
        this.unsigned_count = 0 
        this.reject_count = 0 
} 

/* MAVLink protocol handling class */
${MAVPROCESSOR} = function(logger, srcSystem, srcComponent) {

    this.logger = logger;

    this.seq = 0;
    this.buf = new Buffer.from([]);
    this.bufInError = new Buffer.from([]);
   
    this.srcSystem = (typeof srcSystem === 'undefined') ? 0 : srcSystem;
    this.srcComponent =  (typeof srcComponent === 'undefined') ? 0 : srcComponent;

    this.have_prefix_error = false;

    // The first packet we expect is a valid header, 6 bytes.
    this.protocol_marker = ${PROTOCOL_MARKER};   
    this.expected_length = ${MAVHEAD}.HEADER_LEN;
    this.little_endian = true;

    this.crc_extra = true;
    this.sort_fields = true;
    this.total_packets_sent = 0;
    this.total_bytes_sent = 0;
    this.total_packets_received = 0;
    this.total_bytes_received = 0;
    this.total_receive_errors = 0;
    this.startup_time = Date.now();

    // optional , but when used we store signing state in this object: 
    this.signing = new MAVLinkSigning();
}

// Implements EventEmitter
util.inherits(${MAVPROCESSOR}, events.EventEmitter);

// If the logger exists, this function will add a message to it.
// Assumes the logger is a winston object.
${MAVPROCESSOR}.prototype.log = function(message) {
    if(this.logger) {
        this.logger.info(message);
    }
}

${MAVPROCESSOR}.prototype.log = function(level, message) {
    if(this.logger) {
        this.logger.log(level, message);
    }
}

${MAVPROCESSOR}.prototype.send = function(mavmsg) {
    buf = mavmsg.pack(this);
    this.file.write(buf);
    this.seq = (this.seq + 1) % 256;
    this.total_packets_sent +=1;
    this.total_bytes_sent += buf.length;
}

// return number of bytes needed for next parsing stage
${MAVPROCESSOR}.prototype.bytes_needed = function() {
    ret = this.expected_length - this.buf.length;
    return ( ret <= 0 ) ? 1 : ret;
}

// add data to the local buffer
${MAVPROCESSOR}.prototype.pushBuffer = function(data) {
    if(data) {
        this.buf = Buffer.concat([this.buf, data]);   // python calls this self.buf.extend(c) 
        this.total_bytes_received += data.length;
    }
}

// Decode prefix.  Elides the prefix.
${MAVPROCESSOR}.prototype.parsePrefix = function() {

    // Test for a message prefix.
    if( this.buf.length >= 1 && this.buf[0] != this.protocol_marker ) {

        // Strip the offending initial byte and throw an error.
        var badPrefix = this.buf[0];
        this.bufInError = this.buf.slice(0,1);
        this.buf = this.buf.slice(1);
        this.expected_length = ${MAVHEAD}.HEADER_LEN; //initially we 'expect' at least the length of the header, later parseLength corrects for this. 
        throw new Error("Bad prefix ("+badPrefix+")");
    }

}

// Determine the length.  Leaves buffer untouched.
// Although the 'len' of a packet is available as of the second byte, the third byte with 'incompat_flags' lets
//  us know if we have signing enabled, which affects the real-world length by the signature-block length of 13 bytes.
// once successful, 'this.expected_length' is correctly set for the whole packet.
${MAVPROCESSOR}.prototype.parseLength = function() {
    
    if( this.buf.length >= 3 ) { 
        var unpacked = jspack.Unpack('BBB', this.buf.slice(0, 3)); 
        var magic = unpacked[0]; // stx ie fd or fe etc 
        this.expected_length = unpacked[1] + ${MAVHEAD}.HEADER_LEN + 2 // length of message + header + CRC (ie non-signed length) 
        this.incompat_flags = unpacked[2];  
        // mavlink2 only..  in mavlink1, incompat_flags var above is actually the 'seq', but for this test its ok. 
        if ((magic == ${MAVHEAD}.PROTOCOL_MARKER_V2 ) && ( this.incompat_flags & ${MAVHEAD}.MAVLINK_IFLAG_SIGNED )){ 
            this.expected_length += ${MAVHEAD}.MAVLINK_SIGNATURE_BLOCK_LEN; 
        } 
    }

}

// input some data bytes, possibly returning a new message - python equiv function is called parse_char / __parse_char_legacy 
${MAVPROCESSOR}.prototype.parseChar = function(c) {

    var m = null;

    try {

        this.pushBuffer(c);
        this.parsePrefix();
        this.parseLength();
        m = this.parsePayload();

    } catch(e) {

        this.log('error', e.message);
        this.total_receive_errors += 1;
        m = new ${MAVHEAD}.messages.bad_data(this.bufInError, e.message);
        this.bufInError = new Buffer.from([]);
        
    }

    // emit a packet-specific message as well as a generic message, user/s can choose to use either or both of these.
    if(null != m) {
        this.emit(m._name, m);
        this.emit('message', m);
    }

    return m;

}

// continuation of python's  __parse_char_legacy 
${MAVPROCESSOR}.prototype.parsePayload = function() {

    var m = null;

    // tip: this.expected_length and this.incompat_flags both already set correctly by parseLength(..) above 

    // If we have enough bytes to try and read it, read it.  
    //  shortest packet is header+checksum(2) with no payload, so we need at least that many 
    //  but once we have a longer 'expected length' we have to read all of it. 
    if(( this.expected_length >= ${MAVHEAD}.HEADER_LEN+2) && (this.buf.length >= this.expected_length) ) { 

        // Slice off the expected packet length, reset expectation to be to find a header.
        var mbuf = this.buf.slice(0, this.expected_length);

        // TODO: slicing off the buffer should depend on the error produced by the decode() function
        // - if we find a well formed message, cut-off the expected_length 
        // - if the message is not well formed (correct prefix by accident), cut-off 1 char only
        this.buf = this.buf.slice(this.expected_length);
        this.expected_length = ${MAVHEAD}.HEADER_LEN; // after attempting a parse, we'll next expect to find just a header. 

        try {
            m = this.decode(mbuf);
            this.total_packets_received += 1;
        }
        catch(e) {
            // Set buffer in question and re-throw to generic error handling
            this.bufInError = mbuf;
            throw e;
        }
    }

    return m;

}

// input some data bytes, possibly returning an array of new messages
${MAVPROCESSOR}.prototype.parseBuffer = function(s) {
    
    // Get a message, if one is available in the stream.
    var m = this.parseChar(s);

    // No messages available, bail.
    if ( null === m ) {
        return null;
    }
    
    // While more valid messages can be read from the existing buffer, add
    // them to the array of new messages and return them.
    var ret = [m];
    while(true) {
        m = this.parseChar();
        if ( null === m ) {
            // No more messages left.
            return ret;
        }
        ret.push(m);
    }

}

// from Buffer to ArrayBuffer 
function toArrayBuffer(buf) { 
    var ab = new ArrayBuffer(buf.length); 
    var view = new Uint8Array(ab); 
    for (var i = 0; i < buf.length; ++i) { 
        view[i] = buf[i]; 
    } 
    return ab; 
} 
// and back 
function toBuffer(ab) { 
    var buf = Buffer.alloc(ab.byteLength); 
    var view = new Uint8Array(ab); 
    for (var i = 0; i < buf.length; ++i) { 
        buf[i] = view[i]; 
    } 
    return buf; 
} 
 
//check signature on incoming message , many of the comments in this file come from the python impl
${MAVPROCESSOR}.prototype.check_signature = function(msgbuf, srcSystem, srcComponent) { 

        //if (isinstance(msgbuf, array.array)){ 
        //    msgbuf = msgbuf.tostring() 
        //} 
        if ( Buffer.isBuffer(msgbuf) ) { 
            msgbuf = toArrayBuffer(msgbuf); 
        } 
 
        //timestamp_buf = msgbuf[-12:-6] 
        var timestamp_buf= msgbuf.slice(-12,-6);  
 
        //link_id = msgbuf[-13] 
        var link_id= new Buffer.from(msgbuf.slice(-13,-12)); // just a single byte really, but returned as a buffer 
        link_id = link_id[0]; // get the first byte.
 
        //self.mav_sign_unpacker = jspack.Unpack('<IH') 
        // (tlow, thigh) = self.mav_sign_unpacker.unpack(timestamp_buf) 

        // I means unsigned 4bytes, H means unsigned 2 bytes
        var t = jspack.Unpack('<IH',new Buffer.from(timestamp_buf))  
        const [tlow, thigh]  = t; 
 
        // due to js not being able to shift numbers  more than 32, we'll use this instead.. 
        // js stores all its numbers as a 64bit float with 53 bits of mantissa, so have room for 48 ok. 
        function shift(number, shift) { 
            return number * Math.pow(2, shift); 
        } 
        var thigh_shifted = shift(thigh,32);  
        var timestamp = tlow + thigh_shifted 
 
        // see if the timestamp is acceptable 
 
         // we'll use a STRING containing these three things in it as a unique key eg: '0,1,1' 
        stream_key = new Array(link_id,srcSystem,srcComponent).toString(); 
 
        if (stream_key in this.signing.stream_timestamps){ 
            if (timestamp <= this.signing.stream_timestamps[stream_key]){ 
                //# reject old timestamp 
                //console.log('old timestamp')  
                return false 
            } 
        }else{ 
            //# a new stream has appeared. Accept the timestamp if it is at most 
            //# one minute behind our current timestamp 
            if (timestamp + 6000*1000 < this.signing.timestamp){ 
                //console.log('bad new stream ', timestamp/(100.0*1000*60*60*24*365), this.signing.timestamp/(100.0*1000*60*60*24*365))  
                return false 
            } 
            this.signing.stream_timestamps[stream_key] = timestamp; 
            //console.log('new stream',this.signing.stream_timestamps)  
        } 
 
         //   h = hashlib.new('sha256') 
         //   h.update(this.signing.secret_key) 
         //   h.update(msgbuf[:-6]) 
        var crypto= require('crypto'); 
        var h =  crypto.createHash('sha256'); 
 
        // just the last 6 of 13 available are the actual sig . ie excluding the linkid(1) and timestamp(6) 
        var sigpart = msgbuf.slice(-6); 
        sigpart = new Buffer.from(sigpart); 
        // not sig part 0- end-minus-6 
        var notsigpart = msgbuf.slice(0,-6);  
        notsigpart = new Buffer.from(notsigpart); 

        h.update(this.signing.secret_key); // secret is already a Buffer 
        //var tmp = h.copy().digest(); 
        h.update(notsigpart);  
        //var tmp2 = h.copy().digest() 
        var hashDigest = h.digest(); 
        sig1 = hashDigest.slice(0,6) 
 
        //sig1 = str(h.digest())[:6] 
        //sig2 = str(msgbuf)[-6:] 

        // can't just compare sigs, need a full buffer compare like this... 
        //if (sig1 != sigpart){  
        if (Buffer.compare(sig1,sigpart)){  
            //console.log('sig mismatch',sig1,sigpart)  
            return false 
        } 
        //# the timestamp we next send with is the max of the received timestamp and 
        //# our current timestamp 
        this.signing.timestamp = Math.max(this.signing.timestamp, timestamp) 
        return true
} 

/* decode a buffer as a MAVLink message */
${MAVPROCESSOR}.prototype.decode = function(msgbuf) {

    var magic, incompat_flags, compat_flags, mlen, seq, srcSystem, srcComponent, unpacked, msgId, signature_len; 

    // decode the header
    try {
        """, {'MAVPROCESSOR': get_mavprocessor(xml),
              'MAVHEAD': get_mavhead(xml),
              'PROTOCOL_MARKER': xml.protocol_marker})
    # Mavlink2 only
    if (xml.protocol_marker == 253):
        t.write(outf, """
unpacked = jspack.Unpack('cBBBBBBHB', msgbuf.slice(0, 10));  // the H in here causes msgIDlow to takeup 2 bytes, the rest 1 
        magic = unpacked[0];
        mlen = unpacked[1];
        incompat_flags = unpacked[2];
        compat_flags = unpacked[3];
        seq = unpacked[4];
        srcSystem = unpacked[5];
        srcComponent = unpacked[6];
        var msgIDlow = ((unpacked[7] & 0xFF) << 8) | ((unpacked[7] >> 8) & 0xFF); // first-two msgid bytes 
        var msgIDhigh = unpacked[8];   // the 3rd msgid byte 
        msgId = msgIDlow | (msgIDhigh<<16);  // combined result. 0 - 16777215  24bit number 
        """, {'MAVHEAD': get_mavhead(xml)})
    # Mavlink1
    else:
        t.write(outf, """
unpacked = jspack.Unpack('cBBBBB', msgbuf.slice(0, 6));
        magic = unpacked[0];
        mlen = unpacked[1];
        seq = unpacked[2];
        srcSystem = unpacked[3];
        srcComponent = unpacked[4];
        msgId = unpacked[5];
        """, {'MAVHEAD': get_mavhead(xml)})

    t.write(outf, """
}
    catch(e) {
        throw new Error('Unable to unpack MAVLink header: ' + e.message);
    }

    //  TODO allow full parsing of 1.0 inside the 2.0 parser, this is just a start 
    if (magic == ${MAVHEAD}.PROTOCOL_MARKER_V1){ 
            //headerlen = 6; 
             
            // these two are in the same place in both v1 and v2 so no change needed: 
            //magic = magic; 
            //mlen = mlen; 
 
            // grab mavlink-v1 header position info from v2 unpacked position 
            seq1 = incompat_flags; 
            srcSystem1 = compat_flags; 
            srcComponent1 = seq; 
            msgId1 = srcSystem; 
            // override the v1 vs v2 offsets so we get the correct data either way... 
            seq = seq1; 
            srcSystem = srcSystem1; 
            srcComponent = srcComponent1; 
            msgId = msgId1;  
            // don't exist in mavlink1, so zero-them 
            incompat_flags = 0; 
            compat_flags = 0; 
            signature_len = 0; 
            // todo add more v1 here and don't just return 
            return; 
    } 

    if (magic.charCodeAt(0) != this.protocol_marker) {
        throw new Error("Invalid MAVLink prefix ("+magic.charCodeAt(0)+")");
    }

    // is packet supposed to be signed? 
    if ( incompat_flags & ${MAVHEAD}.MAVLINK_IFLAG_SIGNED ){  
        signature_len = ${MAVHEAD}.MAVLINK_SIGNATURE_BLOCK_LEN; 
    } else { 
        signature_len = 0; 
    } 
 
    // header's declared len compared to packets actual len 
    var actual_len = (msgbuf.length - (${MAVHEAD}.HEADER_LEN + 2 + signature_len)); 
    var actual_len_nosign = (msgbuf.length - (${MAVHEAD}.HEADER_LEN + 2 )); 
 
    if ((mlen == actual_len) && (signature_len > 0)){ 
        var len_if_signed = mlen+signature_len; 
        //console.log("Packet appears signed && labeled as signed, OK. msgId=" + msgId);     
 
    } else  if ((mlen == actual_len_nosign) && (signature_len > 0)){ 
 
        var len_if_signed = mlen+signature_len; 
        throw new Error("Packet appears unsigned when labeled as signed. Got actual_len "+actual_len_nosign+" expected " + len_if_signed + ", msgId=" + msgId);     
 
    } else if( mlen != actual_len) {  
          throw new Error("Invalid MAVLink message length.  Got " + (msgbuf.length - (${MAVHEAD}.HEADER_LEN + 2)) + " expected " + mlen + ", msgId=" + msgId); 

    }  
 
    if( false === _.has(${MAVHEAD}.map, msgId) ) {
        throw new Error("Unknown MAVLink message ID (" + msgId + ")");
    }

    // here's the common chunks of packet we want to work with below.. 
    var headerBuf= msgbuf.slice(${MAVHEAD}.HEADER_LEN); // first10 
    var sigBuf = msgbuf.slice(-signature_len); // last 13 or nothing 
    var crcBuf1 = msgbuf.slice(-2); // either last-2 or last-2-prior-to-signature 
    var crcBuf2 = msgbuf.slice(-15,-13); // either last-2 or last-2-prior-to-signature 
    var payloadBuf = msgbuf.slice(${MAVHEAD}.HEADER_LEN, -(signature_len+2)); // the remaining bit between the header and the crc 
    var crcCheckBuf = msgbuf.slice(1, -(signature_len+2)); // the part uses to calculate the crc - ie between the magic and signature, 

    // decode the payload
    // refs: (fmt, type, order_map, crc_extra) = ${MAVHEAD}.map[msgId]
    var decoder = ${MAVHEAD}.map[msgId];

    // decode the checksum
    var receivedChecksum = undefined; 
    if ( signature_len == 0 ) { // unsigned 
        try { 
            receivedChecksum = jspack.Unpack('<H', crcBuf1); 
        } catch (e) { 
            throw new Error("Unable to unpack MAVLink unsigned CRC: " + e.message); 
        } 
    } else { // signed 
        try { 
            receivedChecksum = jspack.Unpack('<H', crcBuf2); 
        } catch (e) { 
            throw new Error("Unable to unpack MAVLink signed CRC: " + e.message); 
        } 
    }
    receivedChecksum = receivedChecksum[0]; 

    // make our own chksum of the relevant part of the packet... 
    var messageChecksum = ${MAVHEAD}.x25Crc(crcCheckBuf);  
    var messageChecksum2 = ${MAVHEAD}.x25Crc([decoder.crc_extra], messageChecksum); 
 
    if ( receivedChecksum != messageChecksum2 ) { 
        throw new Error('invalid MAVLink CRC in msgID ' +msgId+ ', got 0x' + receivedChecksum + ' checksum, calculated payload checksum as 0x'+messageChecksum2 ); 
    }
 
    // now check the signature... 
    var sig_ok = false 
    if (signature_len == ${MAVHEAD}.MAVLINK_SIGNATURE_BLOCK_LEN){ 
        this.signing.sig_count += 1  
    } 

    // it's a Buffer, zero-length means unused 
    if (this.signing.secret_key.length != 0 ){ 
        var accept_signature = false; 
        if (signature_len == ${MAVHEAD}.MAVLINK_SIGNATURE_BLOCK_LEN){  
            sig_ok = this.check_signature(msgbuf, srcSystem, srcComponent); 
            accept_signature = sig_ok; 
            if (sig_ok){ 
                this.signing.goodsig_count += 1 
            }else{ 
                this.signing.badsig_count += 1 
            } 
            if ( (! accept_signature) && (this.signing.allow_unsigned_callback != undefined) ){ 
                accept_signature = this.signing.allow_unsigned_callback(this, msgId); 
                if (accept_signature){ 
                    this.signing.unsigned_count += 1 
                }else{ 
                    this.signing.reject_count += 1 
                } 
            } 
        }else if (this.signing.allow_unsigned_callback != undefined){ 
            accept_signature = this.signing.allow_unsigned_callback(this, msgId); 
            if (accept_signature){ 
                this.signing.unsigned_count += 1 
            }else{ 
                this.signing.reject_count += 1 
            } 
        } 
        if (!accept_signature) throw new Error('Invalid signature'); 
    } 

    // now look at the specifics of the payload... 
    var paylen = jspack.CalcLength(decoder.format);

    """, {'MAVPROCESSOR': get_mavprocessor(xml),
          'MAVHEAD': get_mavhead(xml)})

    # Mavlink2 only
    if (xml.protocol_marker == 253):
        t.write(outf, """
//put any truncated 0's back in (ie zero-pad ) 
    if (paylen > payloadBuf.length) {
        payloadBuf =  Buffer.concat([payloadBuf, Buffer.alloc(paylen - payloadBuf.length)]);
    }
""")

    t.write(outf, """
    // Decode the payload and reorder the fields to match the order map.
    try {
        var t = jspack.Unpack(decoder.format, payloadBuf); 
    }
    catch (e) {
        throw new Error('Unable to unpack MAVLink payload type='+decoder.type+' format='+decoder.format+' payloadLength='+ payloadBuf +': '+ e.message); 
    }

    // Need to check if the message contains arrays
    var args = {};
    const elementsInMsg = decoder.order_map.length;
    const actualElementsInMsg = JSON.parse(JSON.stringify(t)).length;

    if (elementsInMsg == actualElementsInMsg) {
        // Reorder the fields to match the order map
        _.each(t, function(e, i, l) {
            args[i] = t[decoder.order_map[i]]
        });
    } else {
        // This message contains arrays
        var typeIndex = 1;
        var orderIndex = 0;
        var memberIndex = 0;
        var tempArgs = {};

        // Walk through the fields 
        for(var i = 0, size = decoder.format.length-1; i <= size; ++i) {
            var order = decoder.order_map[orderIndex];
            var currentType =  decoder.format[typeIndex];

            if (isNaN(parseInt(currentType))) {
                // This field is not an array check the type and add it to the args
                tempArgs[orderIndex] = t[memberIndex];
                memberIndex++;
            } else {
                // This field is part of an array, need to find the length of the array
                var arraySize = ''
                var newArray = []
                while (!isNaN(decoder.format[typeIndex])) {
                    arraySize = arraySize + decoder.format[typeIndex];
                    typeIndex++;
                }

                // Now that we know how long the array is, create an array with the values
                for(var j = 0, size = parseInt(arraySize); j < size; ++j){
                    newArray.push(t[j+orderIndex]);
                    memberIndex++;
                }

                // Add the array to the args object
                arraySize = arraySize + decoder.format[typeIndex];
                currentType = arraySize;
                tempArgs[orderIndex] = newArray;
            }
            orderIndex++;
            typeIndex++;
        }

        // Finally reorder the fields to match the order map
        _.each(t, function(e, i, l) {
            args[i] = tempArgs[decoder.order_map[i]]
        });
    }

    

    // construct the message object
    try {
        // args at this point might look like:  { '0': 6, '1': 8, '2': 0, '3': 0, '4': 3, '5': 3 }
        var m = new decoder.type();   // make a new 'empty' instance of the right class,
        m.set(args,false); // associate ordered-field-numbers to names, after construction not during.
    }
    catch (e) {
        throw new Error('Unable to instantiate MAVLink message of type '+decoder.type+' : ' + e.message);
    }

    m._signed = sig_ok; 
    if (m._signed) { m._link_id = msgbuf[-13]; } 
 
    m._msgbuf = msgbuf;
    m._payload = payloadBuf 
    m.crc = receivedChecksum;
    m._header = new ${MAVHEAD}.header(msgId, mlen, seq, srcSystem, srcComponent, incompat_flags, compat_flags);
    this.log(m);
    return m;
}

""", {'MAVHEAD': get_mavhead(xml), 'MAVPROCESSOR': get_mavprocessor(xml), 'PROTOCOL_MARKER' : xml.protocol_marker})

def generate_footer(outf, xml):
    t.write(outf, """

// allow loading as both common.js (Node), and/or vanilla javascript in-browser
if(typeof module === "object" && module.exports) {
    module.exports = {${MAVHEAD}, ${MAVPROCESSOR}};
}

""", {'MAVHEAD': get_mavhead(xml), 'MAVPROCESSOR': get_mavprocessor(xml)})


#--------------------------------------tests start--------

def isfloat(value):
  try:
    float(value)
    return True
  except ValueError:
    return False

def generate_tests_preamble(outf, msgs, args, xml):
    print("Generating preamble")
    t.write(outf, """
/*
TESTS for MAVLink protocol implementation for node.js (auto-generated by mavgen_javascript.py)

Generated from: ${FILELIST}

Note: this file has been auto-generated. DO NOT EDIT
*/
var Long = require('long');

var {${MAVHEAD}, ${MAVPROCESSOR}} = require('./mavlink.js');

// mock mav with sysid-42 and componentid=150
let mav = new ${MAVPROCESSOR}(null, 42, 150);

// this uses the above mock by default, but lets us override it before or during tests if desired
let set_mav = function (_mav) {
    // set global mav var from local
    mav = _mav;
};
exports.set_mav = set_mav;

let verbose = 0; // 0 means not verbose, 1 means a bit more, 2 means most verbose
let set_verbose = function (_v) {
    // set global mav var from local
    verbose = _v;
};
exports.set_verbose = set_verbose;

// relevant to how we pass-in the Long object/s to jspack, we'll assume the calling user is smart enough to know that.
var wrap_long = function (someLong) {
    return [someLong.getLowBitsUnsigned(), someLong.getHighBitsUnsigned()];
}


""", {'FILELIST' : ",".join(args),
      'PROTOCOL_MARKER' : xml.protocol_marker,
      'crc_extra' : xml.crc_extra,
      'WIRE_PROTOCOL_VERSION' : ("2.0" if xml.protocol_marker == 253 else "1.0"),
      'MAVHEAD': get_mavhead(xml),
      'MAVPROCESSOR': get_mavprocessor(xml),
      'HEADERLEN': ("10" if xml.protocol_marker == 253 else "6")}
)


def generate_tests_mavlink_class(outf, msgs, xml):
    print("Generating MAVLink class")

    # Write mapper to enable decoding based on the integer message type
    #t.write(outf, "\n\n${MAVHEAD}.map = {\n", {'MAVHEAD': get_mavhead(xml)});
    for m in msgs:

        outf.write("let test_%s = function () {\n"% (  m.name.lower()));

        #var bs = new mavlink20.messages.battery_status(
        outf.write("   if ( verbose == 2 ) console.log('test creating and packing:%s'); \n" % (  m.name.lower() ) )
        outf.write("   if ( verbose == 1) { process.stdout.write('test creating and packing:"+m.name.lower()+"          \\r'); }\n")
        outf.write("   var test_%s = new %s.messages.%s(); \n" % (  m.name.lower(),get_mavhead(xml), m.name.lower()))
 
        idx = 0; # test data is in same order as ordered_fieldnames
        for f in m.ordered_fieldnames:
            tdata = m.test_data[idx] # test data
            #tdatatype = m.test_data_types[idx] # type of test data 
            fieldtype = m.ordered_fieldtypes[idx] # type of base field
            # wrap things non-number-like as strings, isnumeric() can't handle negatives, but conveniently none of the test suite uses negatives

            #print('testdata:'+tdata);
            #print('tdatatype:'+tdatatype);
            #print('fieldtype:'+fieldtype);
            #if tdatatype != fieldtype:
            #    sys.exit()
            
            _isnum = str(tdata).isdigit()
            _isarray = (tdata[0] == '[')
            _isfloat = isfloat(tdata)

            # javascript inconveniently considers bits >=128 in quite a lot of data types to be unicode, not binary, so we have to understand
            #  these and create them via Buffers and 'binary' or other whacky-doodle-ness here to be sure we get all the tests to pass.

            # array of chars
            if _isarray and (fieldtype == 'char'):
                tdata = 'new Buffer.from('+m.test_data[idx]+').toString("binary")'; # binary encoding here is important for bits >= 128
            # array of uint8_t ( like char )
            elif _isarray and  ( (fieldtype == 'uint8_t') or (fieldtype == 'int8_t')  ):
                tdata = 'new Buffer.from('+m.test_data[idx]+').toString("binary")';  # binary encoding here is important for bits >= 128
            # float/uint16_t/int16_t/int8_t/double array is apparently simple enough without Buffer wrapper
            elif _isarray and ( (fieldtype == 'float') or (fieldtype == 'uint16_t') or (fieldtype == 'int16_t') or (fieldtype == 'double') or ( fieldtype == 'int32_t' ) or ( fieldtype == 'uint32_t' ) ):
                tdata = m.test_data[idx];
            # array of other things
            elif _isarray:
                tdata = 'new Buffer.from('+m.test_data[idx]+') // generic buffer error?';  

            # https://github.com/birchroad/node-jspack/pull/4/commits/9828de064af42ab370009d3eeec7fc11be36b918
            elif fieldtype == 'uint64_t': # unsigned
                tdata =   'wrap_long(Long.fromString("'+m.test_data[idx]+'", true))'; # create unsigned Long from string, then rearrange Long object into 2x32bit unsigned ready for jspack
            elif fieldtype == 'int64_t': # signed
                tdata =   'wrap_long(Long.fromString("'+m.test_data[idx]+'", false))'; # same as above, but signed Long
            # special signed handling, to properly
            elif fieldtype == 'int8_t': # signed fields, we sometimes push raw value/s that exceed the min/max range of signed instead of using the correct sign
                tdata =  '(new Int8Array(['+m.test_data[idx]+']))[0]';  # basically a cast from unsigned int to signed int without sign bit loss
            # special signed handling, to properly
            elif fieldtype == 'int16_t': # signed fields, we sometimes push raw value/s that exceed the min/max range of signed instead of using the correct sign
                tdata =  '(new Int16Array(['+m.test_data[idx]+']))[0]';  # basically a cast from unsigned int to signed int without sign bit loss 
            # special signed handling, to properly 
            elif fieldtype == 'int32_t': # signed fields, we sometimes push raw value/s that exceed the min/max range of signed instead of using the correct sign
                tdata =  '(new Int32Array(['+m.test_data[idx]+']))[0]';  # basically a cast from unsigned int to signed int without sign bit loss

            elif _isfloat:
                    tdata = m.test_data[idx];
            elif _isnum:
                     tdata = m.test_data[idx];   
            else:      
                 #string
                 tdata = '"'+m.test_data[idx]+'"';

            outf.write( "      test_%s.%s = %s;" % ( m.name.lower(),f, tdata) );
            outf.write(" // fieldtype: %s "%(fieldtype));
            outf.write(" isarray: %s \n"%(_isarray));
            idx=idx+1;


        outf.write(" //var t = new Buffer.from([])\n; //%s\n"% (  m.name.lower()));
        outf.write(" var t = new Buffer.from(test_%s.pack(mav));\n"% (  m.name.lower()));

        outf.write("   return [test_%s,t]; // return an array of unpacked and packed options\n"% (  m.name.lower()));
        outf.write("};\n");
        outf.write("exports.test_%s = test_%s; // expose in module\n"% (  m.name.lower() ,m.name.lower() ) );
        outf.write("\n");
    

    outf.write(get_mavhead(xml)+"""Tests = function(){ \n""")

    for m in msgs:
        outf.write("test_%s();\n"% (  m.name.lower()));

    outf.write("};\n");
   
def generate_tests_footer(outf, xml):
    t.write(outf, """

// if run as an app, run the tests immediately, but if run as a module don't, require user to call
if (require.main === module) {
   verbose=2;  // 0 is not verbose, 1 is a bit, 2 is more.
   ${MAVHEAD}Tests();
} 


/* TESTs for MAVLink protocol handling class */
${MAVPROCESSOR}Tests = function() { ${MAVHEAD}Tests(); }
exports.${MAVPROCESSOR}Tests = ${MAVPROCESSOR}Tests; // expose in module

""", {'MAVHEAD': get_mavhead(xml), 'MAVPROCESSOR': get_mavprocessor(xml)})



def generate(basename, xml):
    '''generate complete javascript implementation'''

    if basename.endswith('.js'):
        filename = basename
    else:
        filename = basename + '.js'

    msgs = []
    enums = []
    filelist = []
    for x in xml:
        msgs.extend(x.message)
        enums.extend(x.enum)
        filelist.append(os.path.basename(x.filename))


    for m in msgs:
        m.fielddefaults = []
        if xml[0].little_endian:
            m.fmtstr = '<'
        else:
            m.fmtstr = '>'
        m.native_fmtstr = m.fmtstr

        # we've got instance support in generator, but not in the resultant code, yet.
        m.instance_field = None
        for f in m.ordered_fields:
            m.fmtstr += mavfmt(f)
            if f.instance:
                m.instance_field = f.name
                
        m.order_map = [0] * len(m.fieldnames)
        m.len_map = [0] * len(m.fieldnames)
        m.array_len_map = [0] * len(m.fieldnames)
        m.test_data = [0] * len(m.fieldnames)
        m.test_data_types = [0] * len(m.fieldnames)

        for i in range(0, len(m.fieldnames)):
            m.order_map[i] = m.ordered_fieldnames.index(m.fieldnames[i])
            m.ordered_fieldtypes[i] = m.ordered_fieldtypes[i]
            m.test_data[i] = str(m.ordered_fields[i].test_value)
            m.test_data_types[i] = str(m.ordered_fields[i].type)
            m.array_len_map[i] = m.ordered_fields[i].array_length
            
        for i in range(0, len(m.fieldnames)):
            n = m.order_map[i]
            m.len_map[n] = m.fieldlengths[i]





    print("Generating %s" % filename)
    outf = open(filename, "w")
    generate_preamble(outf, msgs, filelist, xml[0])
    generate_enums(outf, enums, xml[0])
    generate_message_ids(outf, msgs, xml[0])
    generate_classes(outf, msgs, xml[0])
    generate_mavlink_class(outf, msgs, xml[0])
    generate_footer(outf, xml[0])
    outf.close()
    print("Generated %s OK" % filename)

    testfilename = filename.replace('.js','.tests.js')
    print("Generating TESTS %s" % testfilename)
    outf = open(testfilename, "w")
    generate_tests_preamble(outf, msgs, filelist, xml[0])
    generate_tests_mavlink_class(outf, msgs, xml[0])
    generate_tests_footer(outf, xml[0])
    outf.close()
    print("Generating TESTS %s" % testfilename)

